Module 2 Flashcards
(29 cards)
What do B-cells differentiate into?
Plasma cells
What is the B-cell type when Ab is present on surface?
naive B-cell
In a light chain what regions are there?
variable region and constant region
What region contains the Ag binding site?
variable region
Approximate weight of an antibody?
150kDa
2x ~50kDa heavy chains and 2x ~25 kDa light chains
What is an epitope?
Specific region of an antigen that interacts with an antibody. Most antigens are multivalent, more than 1 epitope. Can be different epitopes or repeated epitopes
What does proteolytic cleavage by papain do?
Cut the antibody into Fab x2 and 1 Fc. Fc has disulfide bond remaining on Fc
What does proteolytic cleavage by pepsin do?
Cut the antibody into 2x F(ab’)2 connected by disulfied bond. 1 pFc’ produced which is partially cleaved into small fragments
Where is paratope located?
In the Fab region where epitope will bind to.
Is it B-sheets or a-helices forming paratope?
Loops in B-sheets
What is the hypervariable region?
The light chains’ V-region, also known as CDR’s
They form the Ag binding site
There is variation from these loops
The two type of epitopes?
Linear epitope
Discontinuous epitope: conformational epitopes where proteins are folded together.
What are the 5 Ig isotypes?
These 3 isotypes have 4 heavy chains+ hinge + disulphide bond
IgG - gamma
IgD - delta
IgA -alpha
These 2 isotypes have 5 heavy chains, no hinge nor disulphide bond
IgM - mu
IgE - epsilon
Explain isotypic, allotypic and idiotypic differences
Allotypic - antibody different to someone elses due to genetic difference between each other
Idiotypic - same isotype but specific for different epitopes
What isotype has hinge variability and subclasses?
IgG. There is IgG1 which looks like typical antibody, IgG2 with 3 disulphide bonds, IgG3 with many disulphide bonds, and IgG4 (just 3 amino acids smaller than IgG1).
Say you have a precipitation reaction of a pool of antigen and antibody and there is a small zone where precipitate has formed, what is this called?
Zone of equivalence. Equal molar ration of epitope and paratope
What is antigen-independency? Prior to exposure of antigen to antibody.
Antigen-dependent: This happens during B-cell development in the bone marrow, your body prepping a massive antibody library just in case something nasty shows up later.
This includes
Combinatorial diversity: Random recombination of V (variable), D (diversity), and J (joining) gene segments for the heavy chain
Random V and J recombination for the light chain.
Junctional diversity: Extra variability at the joining sites of V, D, J through: P-nucleotide addition (palindromic), and N-nucleotide addition (by TdT enzyme). Changes in sequences.
Results in millions of different B-cell receptors (BCRs) with unique binding sites
What is antigen-dependency? Following exposure to an antigen.
In the germinal center of lymph nodes, and the immune system is tailoring the response to the actual invader.
This includes:
Somatic hypermutation: Tiny mutations in the variable region of BCR, specifically CDRs
What is an RSS and what rule does it follow?
A combination of a nonamer, spacer, or hepator. Recombination here is guided by 12/23 rule. An RSS spacer with 23bp can join RSS 12bp. This stops a V section combining with another V section.
What enzyme is used in junctional diversity?
TdT which randomly adds nucleotides
What happens when a naive B-cell encounters its first antigen?
- Somatic hypermutation:
- Occurs during humoral response to pathogenic infection
- B-cells migrate to primary follicle of lymph node and establish a germinal centre
- somatic hypermutation occurs during proliferation
- enhances affinity of antibodies for antigen particularly during secondary and subsequent responses. Increase in Ab
Enzyme called AID, converts C to U which are then converted by any other nucleotide. Occurs in variable chain
Somatic hypermutation leads to?
Affinity maturation - A bunch of B cells (B1, B2..B7) competing with each other for occupying that germinal centre. If one B-cell has better binding to antigen, better kickstart for that B-cell & low affinity B-cells will stop proliferating.
Where will the mutations like to occur and how long of primary immunisation to increase affinity?
In the loops of the CDR’s. About 2 weeks.
What is allelic exclusion in Ig expression?
Ensures that each B-cell expresses only one functional Ig heavy and light chain, preventing multiple antigen specificities.
